Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$175.95	4.312%	$183.537	$183.54	$183.55	$183.50
Purchase #2	$128.45	11.692%	$143.4684	$143.47	$143.45	$143.50
Purchase #3	$60.28	12.143%	$67.5998	$67.60	$67.60	$67.60
Purchase #4	$142.50	8.693%	$154.8875	$154.89	$154.90	$154.90
Purchase #5	$37.33	13.858%	$42.5032	$42.50	$42.50	$42.50
Purchase #6	$18.99	9.444%	$20.7834	$20.78	$20.80	$20.80
Purchase #7	$190.58	4.371%	$198.9103	$198.91	$198.90	$198.90
7 purchase totals =	$754.08		$811.6896	$811.69	$811.70	$811.70